Antennas are deployed in many applications, and in many different configurations, to receive and transmit electromagnetic energy. Configurations range from basic monopole and dipole wire antennas to complex antenna arrays having multiple elements.
In any such configurations, the antenna or elements making up the antenna must be able conduct electrical signals and currents so that electromagnetic energy can be transmitted and/or received. In addition, the supporting structure of the antenna or antenna elements typically have sufficiently high electrical conductivity to provide shielding for electronics within the structure and to provide electrical symmetry. Given these conductivity requirements, most antennas and antenna structures are fabricated from metals, which generally have good conductive qualities.
One significant problem associated with using metal in antenna systems is that metal generally produces a high degree of reflections of incoming radar signals. Such reflections are sometimes referred to as backscatter or retroreflections. In certain applications, these reflections are undesirable, particularly in applications such as stealth operations or in those applications where low detectability of a deployed antenna system is necessary. This is because the reflections are sent back toward other antennas and/or tracking radars, and can therefore increase a host platform's radar cross section (RCS) caused by the increased RCS of the antenna system causing the reflections. In short, the reflections can be used to identify, track, and/or target the system(s) causing the reflections.
Recently, polymer materials having sufficiently high electrical conductivities have been developed and are commercially available. Examples of such materials include polypyrrole, polycarbazole, polyaniline, polyacetylene, and polythiophene. The electrical conductivity level of these materials can be varied significantly as a function of the dopant level applied to the polymers. This dopant level is determined or otherwise set during the manufacturing process of the polymer. The doped and now conductive polymers can then be used as a coating over materials like fiberglass to provide an electrically conductive composite material that can be used to form parts of the antenna system, thereby reducing that system's effective radar cross section.
However, conventional polymer antenna systems still rely on metallic materials for transmitting and receiving, which remain a significant cause of reflections. For example, metal material is typically used as one of the constituents that form the polymer composite material, or metal coatings or tips are used on the antenna elements in conjunction with the polymer composite. Thus, undesirable reflections (e.g., backscatter and retroreflections) are still a problem for conventional polymer composite antenna systems.
Moreover, significant differences in dielectric constants associated with conventional antenna systems cause lower antenna efficiency. Antenna efficiency is reduced by incident signal that is not captured by the antenna, but re-radiated. Differences in dielectric constants inhibits some of the electromagnetic energy signals of interest from being captured by the antenna system, which in turn reduces antenna efficiency. This relationship between antenna efficiency and high conductivity represents a longstanding trade that is acceptable for many antenna systems. However, given more demanding requirements associated with today's communication systems, greater efficiencies are desirable.
What is needed, therefore, are polymer antenna structures having low reflectivity and high efficiency.